1. Field of the Invention
The present invention relates to a measuring machine such as a three-dimensional measuring machine and coordinates measuring machine. More specifically, it relates to a measuring machine having a base, a probe and a moving mechanism for relatively moving the base and the probe, in which accuracy with respect to temperature change is guaranteed, and furthermore, a accuracy-guaranteed temperature range can be extended.
2. Description of Related Art
Conventionally, a measuring machine such as three-dimensional measuring machine and coordinates measuring machine has been known for measuring profile and dimension of a workpiece. Generally, such measuring machine has a base, a probe, a moving mechanism for moving the probe relative to the base in three-dimensional directions (X, Y and Z-axis directions), and a controller for; controlling the movement of the moving mechanism; for acquiring coordinate value of respective axes when the probe contacts the workpiece and; for measuring the dimension of the workpiece based on the coordinate values.
Usually, main structural members such as the base and the moving mechanism of this type of measuring machine are made of materials having rigidity required for the respective components.
For instance, the base is made of stone, ceramics and castings and has a covering member for covering the circumference thereof. Both leg portions of a portal frame of the moving mechanism is made of castings, and beam spanning between upper ends of the legs is made of ceramics, the combination of the parts constituting the moving mechanism.
However, since the conventional measuring machine uses different material having rigidity required for respective portions, geometrical accuracy in temperature change is deteriorated.
The deterioration in the geometrical accuracy is thought to be caused by following reasons:
(1) Deterioration in geometrical accuracy according to difference in temperature distribution inside the machine
Since the conventional measuring machine uses different material having rigidity required for respective portions, thermal conductivity differs in respective portions, thereby making the temperature distribution inside the machine uneven to deteriorate geometrical accuracy.
(2) Deterioration in geometrical accuracy by attaching difference members
Since members having different thermal expansion coefficient are directly attached in respective portions of the conventional measuring machine, the expansion amount of respective members differ when the temperature changes, thereby causing the deterioration of the geometrical accuracy.
Some of the three-dimensional measuring machines have temperature correcting function, which try to expand the range of temperature in which the accuracy is guaranteed.
However, the temperature correcting function can not effectively performed as long as the aforesaid problem (deterioration of geometrical accuracy in temperature change) is not solved.
The object of the present invention is to provide a measuring machine for guaranteeing the geometrical accuracy in temperature change, thereby guaranteeing the accuracy in temperature accuracy and extending the range of temperature in which the accuracy is guaranteed.
A measuring machine according to the present invention has a base, a probe and a moving mechanism for relatively moving the base and the probe. The measuring machine is characterized in that a main structural member of the moving mechanism is made of aluminum or aluminum alloy including aluminum as main component.
According to the above arrangement, since the main structural member of the moving mechanism is made of aluminum or aluminum alloy including aluminum as main component, which have large thermal conductivity, temperature tracking ability against the temperature change can be improved, thereby making uniform temperature distribution of the entire machine.
For instance, when the moving mechanism is made of a portal frame, a slider and a Z-axis spindle, the portal frame, the slider and the Z-axis spindle may be made of aluminum or aluminum alloy including aluminum as main component to make temperature distribution of the main structural member of the moving mechanism to be uniform.
Accordingly, since the deterioration in geometrical accuracy in accordance with the temperature change can be restrained, the accuracy can be guaranteed irrespective of the temperature change and the accuracy-guaranteed temperature range can be extended.
In the above, the moving mechanism preferably has first moving mechanism for linearly moving the probe, second moving mechanism for moving the probe in a direction orthogonal with the moving direction of the first moving mechanism, and third moving mechanism for moving the probe in a direction orthogonal with the moving direction of the first moving mechanism and the second moving mechanism.
Accordingly, the probe can be moved in three-dimensional directions, thereby highly accurately measuring three-dimensional dimension of the workpiece.
Further, at least one of the first, the second and the third moving mechanism preferably has a guide member fixed along the moving direction thereof, a slider movably provided to the guide member, a feed screw axis disposed to the guide member along the moving direction of the slider and having both ends being fixed to the guide member, and a nut member screwed to the feed screw axis for moving the slider in a longitudinal direction of the feed screw axis by a rotation of the feed screw axis, the guide member being formed of aluminum or aluminum alloy having aluminum as main component, and the feed screw axis being formed of steel and having an end portion supported to be slidable in an axial direction thereof.
According to the above arrangement, since the feed screw axis can be slid in the axial direction thereof even when the guide member and the feed screw causes difference in expansion amount in accordance with the temperature change, the disadvantage caused by the difference of the thermal expansion rate of the guide member and the feed screw axis can be eliminated.
Further, since the guide member is formed of aluminum or aluminum alloy having aluminum as main component, the temperature distribution of the main structural member of the moving mechanism can be made uniform. On the other hand, since the feed screw axis is formed of steel having large rigidity, the slide accuracy of the slider can be secured.
When a member attached to the main structural member of the moving mechanism is made of a material other than aluminum or aluminum alloy having aluminum as main component, an elastic member is preferably inserted to the attachment portion of the main structural member and the member attached thereto.
Accordingly, even when the main structural member and the member attached thereto cause difference in expansion amount in accordance with the temperature change, the difference can be absorbed by the elastic deformation of the elastic member, thereby solving the disadvantage caused by the difference in thermal expansion rate between the main structural member and the member attached thereto.
Further, when the member attached to the main structural member of the moving mechanism is made of a material other than aluminum and aluminum alloy including aluminum as main component, the member attached to the main structural member of the moving mechanism preferably has an easily elastically deforming portion.
Also in the above, even when the main structural member and the member attached thereto cause difference in expansion amount in accordance with the temperature change, the difference can also be absorbed by the elastic deformation of the elastic member, thereby solving the disadvantage caused by the difference in thermal expansion rate between the main structural member and the member attached thereto.
Another measuring machine according to the present invention has a base, a probe and a moving mechanism for relatively moving the base and the probe, the base having a cover for covering the periphery thereof and a fan for circulating air to an inside and an outside of the cover.
Accordingly, since the temperature distribution inside the cover for covering the base can be made uniform by the fan, the geometrical accuracy in temperature change can be guaranteed.
Still another measuring machine according to the present invention has a base, a probe, a moving mechanism for moving the probe relative to the base, and a controller for controlling the movement of the moving mechanism. The measuring machine is characterized in having a thermal insulating cover for covering the controller and a fan for discharging waste heat from the controller to an outside thereof.
According to the above, since the heat from the controller can be discharged to the outside by the fan, the bad influence by the heat can be restrained to the utmost, thereby also guaranteeing geometrical accuracy in temperature change.